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<p><code>MySQL</code>中定义数据类型对数据库的优化是非常重要的，在<code>MySQL</code>中的数据类型大致可以分为三类：</p> <ul><li>数值类型</li> <li>字符类型</li> <li>时间类型</li></ul> <h2 id="数值类型"><a href="#数值类型" class="header-anchor">#</a> 数值类型</h2> <table><thead><tr><th style="text-align:center;">类型</th> <th style="text-align:center;">大小及范围</th> <th style="text-align:center;">作用</th></tr></thead> <tbody><tr><td style="text-align:center;"><code>tinyint(m)</code></td> <td style="text-align:center;">1个字节  范围(-128~127)</td> <td style="text-align:center;">小整数</td></tr> <tr><td style="text-align:center;"><code>smallint(m)</code></td> <td style="text-align:center;">2个字节  范围(-32768~32767)</td> <td style="text-align:center;">大整数</td></tr> <tr><td style="text-align:center;"><code>mediumint(m)</code></td> <td style="text-align:center;">3个字节  范围(-8388608~8388607)</td> <td style="text-align:center;">大整数</td></tr> <tr><td style="text-align:center;"><code>int(m)</code></td> <td style="text-align:center;">4个字节  范围(-2147483648~2147483647)</td> <td style="text-align:center;">大整数</td></tr> <tr><td style="text-align:center;"><code>bigint(m)</code></td> <td style="text-align:center;">8个字节  范围(+-9.22*10的18次方)</td> <td style="text-align:center;">极大整数</td></tr> <tr><td style="text-align:center;"><code>float(m,d)</code></td> <td style="text-align:center;">4个字节 8位精度 m总个数，d小数位</td> <td style="text-align:center;">单精度浮点数值</td></tr> <tr><td style="text-align:center;"><code>double(m,d)</code></td> <td style="text-align:center;">8个字节 16位精度 m总个数，d小数位</td> <td style="text-align:center;">双精度浮点型</td></tr> <tr><td style="text-align:center;"><code>decimal(m,d)</code></td> <td style="text-align:center;">参数m是总个数，d是小数位</td> <td style="text-align:center;">定点数</td></tr></tbody></table> <p>关于浮点数<code>float</code>,<code>double</code>,<code>decimal</code>,的区别：<code>float</code>在内存中占用4个字节，而<code>double</code>在内存中占用8个字节，所以<code>float</code>的精度没有<code>double</code>高，但是同等条件下CPU处理单精度浮点数的效率要高。</p> <p>在存储同样范围值时，通常<code>decimal</code>使用的空间更少，一般在存储金额时会使用<code>decimal</code>。</p> <p>浮点型在数据库中存放的是近似值，而定点类型在数据库中存放的是精确值。</p> <h2 id="字符类型"><a href="#字符类型" class="header-anchor">#</a> 字符类型</h2> <table><thead><tr><th style="text-align:center;">类型</th> <th style="text-align:center;">大小</th> <th style="text-align:center;">说明</th></tr></thead> <tbody><tr><td style="text-align:center;"><code>char</code></td> <td style="text-align:center;">0-255字节</td> <td style="text-align:center;">定长字符串</td></tr> <tr><td style="text-align:center;"><code>varchar</code></td> <td style="text-align:center;">0-65535 字节</td> <td style="text-align:center;">变长字符串</td></tr> <tr><td style="text-align:center;"><code>tinyblob</code></td> <td style="text-align:center;">0-255字节</td> <td style="text-align:center;">不超过 255 个字符的二进制字符串</td></tr> <tr><td style="text-align:center;"><code>tinytext</code></td> <td style="text-align:center;">0-255字节</td> <td style="text-align:center;">短文本字符串</td></tr> <tr><td style="text-align:center;"><code>blob</code></td> <td style="text-align:center;">0-65535字节</td> <td style="text-align:center;">二进制形式的长文本数据</td></tr> <tr><td style="text-align:center;"><code>text</code></td> <td style="text-align:center;">0-65535字节</td> <td style="text-align:center;">长文本数据</td></tr> <tr><td style="text-align:center;"><code>mediumblob</code></td> <td style="text-align:center;">0-16777215字节</td> <td style="text-align:center;">二进制形式的中等长度文本数据</td></tr> <tr><td style="text-align:center;"><code>mediumtext</code></td> <td style="text-align:center;">0-16777215字节</td> <td style="text-align:center;">中等长度文本数据</td></tr> <tr><td style="text-align:center;"><code>longblob</code></td> <td style="text-align:center;">0-4294967295字节</td> <td style="text-align:center;">二进制形式的极大文本数据</td></tr> <tr><td style="text-align:center;"><code>longtext</code></td> <td style="text-align:center;">0-4294967295字节</td> <td style="text-align:center;">极大文本数据</td></tr></tbody></table> <ul><li><code>char</code>类型是定长的,而<code>varchar</code>是变长的，<code>char(m)</code>存储的值长度小于<code>m</code>时，<code>MySQL</code>会在其右边用空格补足，而<code>varchar</code>存储的值是只占用值得本身大小加上一个记录长度的一个字节。<code>char</code>在处理速度上要比<code>varchar</code>快，但是比较占用存储空间</li> <li><code>blob</code> 和 <code>text</code> 都是为存储<strong>很大的数据</strong>而设计的数据类型，分别采用二进制和字符方式存储。</li></ul> <h2 id="日期时间类型"><a href="#日期时间类型" class="header-anchor">#</a> 日期时间类型</h2> <table><thead><tr><th style="text-align:center;">类型</th> <th style="text-align:center;">大小</th> <th style="text-align:center;">说明</th></tr></thead> <tbody><tr><td style="text-align:center;"><code>date</code></td> <td style="text-align:center;">3个字节</td> <td style="text-align:center;">以YYYY-MM-DD的格式显示，比如：2009-07-19</td></tr> <tr><td style="text-align:center;"><code>time</code></td> <td style="text-align:center;">3个字节</td> <td style="text-align:center;">以HH:MM:SS的格式显示。比如：11：22：30</td></tr> <tr><td style="text-align:center;"><code>year</code></td> <td style="text-align:center;">1个字节</td> <td style="text-align:center;">以YYYY的格式显示如：2019</td></tr> <tr><td style="text-align:center;"><code>datetime</code></td> <td style="text-align:center;">8个字节</td> <td style="text-align:center;">以YYYY-MM-DD HH:MM:SS的格式显示如：2019-09-19 12：11：11</td></tr> <tr><td style="text-align:center;"><code>timestamp</code></td> <td style="text-align:center;">4个字节</td> <td style="text-align:center;">以YYYY-MM-DD HH:MM:SS的格式显示，比如：2019-08-19 12：11：11</td></tr></tbody></table> <p><code>timestamp</code>存储和时区相关，即会根据时区做转换,而<code>datetime</code>存储和时区不相关，不会做转换;</p> <hr> <p><strong>参考文献</strong></p> <ul><li><a href="https://www.cnblogs.com/ypha/p/14018470.html" target="_blank" rel="noopener noreferrer">浅谈MySQL中float、double、decimal三个浮点类型的区别与总结<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" 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